Typical IEEE 802.11-based WLAN NIDs have two power modes—a “constant active mode” (CAM), in which the device is always “awake,” and a standard-defined “power saving mode” (PSM), in which the device is “asleep” most of the time and awakens periodically, e.g., every 100 ms.
In the CAM, application performance, in terms of packet throughput and latency, for example, may be very good. Because the NID is always awake, however, power consumption in CAM tends to be very high. In the PSM, power consumption is much lower, but at the cost of performance because data that arrives while the NID is asleep tends to be delayed. Because the NID is awake only periodically, there is no correlation, generally speaking, between the times at which the NID is awake, and the times at which data is being delivered through the NID. Consequently, though the PSM may provide power savings, it is well known that this kind of operation affects the downlink application's performance significantly and tends to degrade quality of service (QoS). It would be desirable, however, to be able to save as much power as possible while maintaining acceptable performance, i.e., to be able to optimize the tradeoff between power and performance.
Smart power management, where the operating system awakens the NID based on some intelligence about when data is to be received, is relatively easy for typical uplink applications because round trip time (RTT) information may be known for each packet. Consequently, the operating system knows the packet arrival times, and, accordingly, when to awaken the NID to receive data.
In typical IEEE 802.11-based WiFi systems, however, downlink applications, such as web browsing, FTP, and video streaming, for example, are dominant. Unfortunately, for typical downlink applications, the RTT may be unknown, and smart power management systems that work for uplink applications might not work well for downlink applications. It would be advantageous, therefore, if there were available systems and methods for smart power management that strike a desired balance between power savings and performance for downlink applications.